JP2007020915A - Ultrasonic diagnostic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a new technique for improving a frame rate of a color Doppler in ultrasonic diagnosis. <P>SOLUTION: TxDBF (transmission beam former)12 and 14 generate pulse-type ultrasonic waves to be transmitted simultaneously in directions different from each other. A piezoelectric element array 22 carries out corresponding ultrasonic transmission, and receives its reflected waves. By repeating the series of processing several times by fixing the directions, received signals for several times with regard to each direction are obtained, and spatial velocity distribution is obtained based on analysis of their phase relation. The waveforms of the pulse-type ultrasonic waves to be transmitted in the different directions simultaneously are set so that at least center frequencies may be equal to each other. Thus, the properties of Doppler shift frequencies varying according to the center frequencies are made to be common, so that receiving processing such as aliasing is simplified. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for obtaining a spatial distribution of Doppler information by repeatedly transmitting and receiving ultrasonic waves in the same direction.

  In ultrasonic diagnosis, measurement for obtaining a velocity space distribution such as blood flow in a measurement target is often performed. In this measurement, a spatial velocity distribution is obtained by performing ultrasonic wave transmission / reception a plurality of times in the same direction and repeating the process of calculating the velocity based on the phase relationship between the received signals in each direction. The measurement results are displayed on the normal display screen in real time, and are called color Doppler, power Doppler, black-and-white Doppler, tissue Doppler, etc. from the display mode.

  For example, in a color Doppler image, information on the velocity of blood flow or tissue movement and the received signal power from the blood flow or moving tissue is usually displayed on a black and white tomographic image (also called a B-mode image or a black and white image). Displayed in color. A black-and-white tomographic image is an image that is generally created based on ultrasonic scanning in which transmission / reception is performed only once in each direction, and shows a (static) structure inside a diagnosis target.

In this method, the frame rate f _R of the color Doppler image is expressed by the following equation: f _R = c / {(N _BWB + N _CFB * N _P ) * 2 * L _D }}
Here, N _BWB beam direction number of the tomographic image for per frame, N _CFB beam direction number used in the color Doppler diagnostic per frame, N _P is the number of transmission repetitions in one direction of the color Doppler diagnostic (1 If a series of transmissions in the direction is regarded as a packet, it can be interpreted as the number of transmission repetitions per packet), L _D represents a diagnostic distance, and c represents an average sound speed (generally sound speed in water) in the measurement target. .

In order to diagnose blood flow in a fast-moving organ such as the heart with color Doppler, high time resolution is required. An example is a diagnosis of a child's heart. In such a case, conventionally, the diagnostic distance L _D is shortened to increase the transmission repetition frequency, the azimuth direction diagnostic area is narrowed, and the transmission beam density (the number of transmission directions per image) is reduced. Lowering was also done.

  However, if the diagnostic distance is shortened, it becomes impossible to detect deep information. Further, when the diagnosis area is narrowed, information on the azimuth direction is lost. Further, when the transmission beam density is lowered, the spatial resolution in the azimuth direction is lowered. In the following, based on these problems, documents related to technical improvements made for the purpose of improving the frame rate will be briefly described.

  The technique of the following Patent Document 1 is intended to improve real-time characteristics by linear electronic scanning, and simultaneously transmits pulses in different directions between even-numbered elements and odd-numbered elements of a transducer array, By simultaneously receiving the received signals, a double frame rate is realized. Patent Document 2 below discloses a technique of simultaneously transmitting transmission waveforms in different frequency bands in different directions between even-numbered elements and odd-numbered elements of a transducer array.

  Patent Document 3 below discloses a technique for improving time resolution by simultaneously transmitting two different frequency modulated waves in different directions. In Patent Document 4 below, a mode is described in which transmission waveforms of two different frequency bands are simultaneously transmitted in different directions to improve time resolution.

  However, in the techniques of Patent Documents 1 and 2, since the element pitch used for transmission in the same direction becomes coarse, when the ultrasonic beam is steered, the high frequency component is reduced, and the spatial resolution in the azimuth direction is reduced. This leads to a decrease in detection sensitivity. Further, when the opening size is the same as the conventional size, the number of transmitting elements is halved, so that the transmission sound pressure per direction is reduced. However, if an attempt is made to compensate for the decrease in sound pressure by increasing the transmission amplitude, there is a risk of causing heat generation of the probe.

  The Doppler shift frequency is determined depending on the transmission center frequency. For this reason, in the techniques of Patent Documents 2 to 3, even when the blood flow velocities are equal, the aliasing of the frequency due to aliasing occurs first in the reception result for the transmission with a high center frequency. . Since correction of aliasing generally requires a complicated procedure, it is not preferable to perform individual correction processing for each direction in such a case. Further, the techniques of Patent Documents 2 to 4 have a problem in that a difference in detection sensitivity occurs in each direction due to the fact that ultrasonic attenuation in a measurement target such as a living body depends on the frequency. As described above, in the conventional technique, it is difficult to improve the frame rate and the spatial uniformity in obtaining the velocity space distribution such as blood flow.

  Patent Document 5 below also discloses a technique for transmitting ultrasonic waves in different directions at the same time. Here, for each transmitted ultrasonic beam, the frame rate is improved by setting a plurality of reception focal points and acquiring reception signals in a plurality of adjacent directions. However, this technique has been made to obtain a tomographic image, and no mention is made of color Doppler.

Japanese Patent No. 2760558 Japanese Patent No. 3356996 Special Table 2002-539877 Japanese Patent Laid-Open No. 8-38473 JP 2002-336246 A

  An object of the present invention is to establish a new technique for improving the frame rate in obtaining the velocity space distribution of blood flow and moving tissue by ultrasonic diagnosis.

  Another object of the present invention is to improve the spatial uniformity without narrowing the diagnostic area while suppressing the increase in probe input power when obtaining the velocity space distribution of blood flow and moving tissue by ultrasonic diagnosis. Develop technology to achieve.

  Still another object of the present invention is to simplify the received signal processing in determining the velocity space distribution of blood flow and moving tissue by simultaneous multi-directional transmission of ultrasonic waves.

  The ultrasonic diagnostic apparatus of the present invention repeats a series of processes of transmitting pulsed ultrasonic waves simultaneously in a plurality of directions and receiving a reflected wave from a reflector a plurality of times, and obtains a received signal for a plurality of times in each direction. An acquisition means and a calculation means for calculating the spatial distribution of the reflector velocity in each direction based on the phase analysis between the received signals, and the pulse-type ultrasonic wave transmitted simultaneously in a plurality of directions in the acquisition means, The center frequencies are set equal to each other.

  The acquisition unit typically controls an ultrasonic probe in which a large number of ultrasonic transducers are arranged in an array, and performs ultrasonic transmission / reception with respect to a measurement target (for example, a living body such as a human). In transmission, pulsed ultrasonic waves are transmitted simultaneously in a plurality of directions, and in reception, reflected ultrasonic waves reflected by the reflector in each direction are received. The acquisition unit repeats this process a plurality of times to acquire a reception signal corresponding to a plurality of transmissions in each direction. Note that pulse-type ultrasonic waves transmitted simultaneously in a plurality of directions by the acquisition means are set to have the same center frequency.

  The calculation means analyzes a plurality of received signals obtained in each direction to obtain a velocity distribution of the reflector in those directions. The speed is calculated by analyzing the phase relationship between the received signals.

  According to this configuration, since ultrasonic transmission is performed simultaneously in a plurality of directions, a high frame rate can be secured and the spatial distribution of speed can be obtained. Moreover, since the center frequencies of the ultrasonic waves transmitted in a plurality of directions are set to the same value, the Doppler shift frequency corresponding to the speed of the reflector is associated with the speed on the same scale in each direction. Therefore, it is possible to obtain the velocity distribution by performing similar signal processing without performing special processing for each direction. As a result, since the time for signal processing is reduced, the frame rate in ultrasonic diagnosis can be improved without narrowing the diagnosis area.

  In the case of sector scanning, different directions are typically given an angle difference (for example, 20 degrees or more) so as to reduce interference of transmission waveforms between the directions. The obtained spatial distribution of speed is typically displayed on a display device (which may be built-in or separately provided) with appropriate coloring. The display is usually performed by superimposing on the black and white tomographic image data obtained by ultrasonic transmission / reception performed between the above processes.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, the acquisition unit repeatedly acquires the reception signal while changing the transmission direction of the pulse-type ultrasonic wave so as to scan the set scanning region, and the calculation unit performs the scanning. Obtain the spatial distribution of the reflector velocity in the region. This makes it possible to obtain a two-dimensional or three-dimensional velocity distribution for the scanning region.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, in the analysis of the phase relationship by the calculating means, processing is performed on the assumption that the same folding frequency is set for each direction. In general, the Doppler shift changes depending on the center frequency of transmission, and aliasing occurs when the Doppler shift exceeds half of the pulse repetition frequency. Therefore, if the transmission center frequency and the pulse repetition frequency are different for each direction, the aliasing conditions are different. In order to correct this on the processing side, complicated processing is required. However, since the Doppler shift frequency characteristics are made common by setting the center frequencies of the transmission waves in the respective directions to be equal, it is possible to make the aliasing frequency setting in the aliasing process common.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, ultrasonic transmission in the acquisition unit is performed at different focal lengths in each direction. Moreover, in one aspect of the ultrasonic diagnostic apparatus of the present invention, the ultrasonic transmission in the acquisition unit is performed with different energy intensities according to the focal length in each direction. That is, usually, ultrasonic transmission is performed with high energy intensity when the focal distance is deep, and ultrasonic transmission is performed with low energy intensity when the focal distance is shallow. As a result, the reflected wave from a deep position can be received with a sufficient magnitude, and the reception sensitivity increases. On the other hand, by not applying excessively large energy to ultrasonic transmission to a shallow position, it is possible to suppress the total energy and reduce the heat generation of the probe.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, the focal length is changed at least once in a plurality of ultrasonic transmissions in each direction in the acquisition means. This makes it possible to obtain a highly accurate velocity distribution for both a relatively shallow region and a relatively deep region.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, the ultrasonic transmission in the acquisition unit is performed with the same transmission waveform in each direction. When the transmission waveforms are the same, the center frequencies match, and the frequency bandwidths also match. Therefore, commonality of Doppler shift characteristics in each direction is increased.

  In one aspect of the ultrasonic diagnostic apparatus of the present invention, a pulse compression technique is used for ultrasonic transmission / reception in the acquisition means. Pulse compression can be performed in various ways. Specifically, an example using a linear or nonlinear FM signal can be given. Further, the transmission waveform may have a coarse resolution in the amplitude direction, or may be a binary waveform in an extreme case. In addition, it is possible to use a signal obtained by phase-modulating a carrier frequency using a binarized code as a transmission waveform. Examples of the binarized code include an M series, a Baker series, a Gold series, a Golay series, and the like.

  FIG. 1 is a block diagram schematically showing the configuration of an ultrasonic diagnostic apparatus 10 according to the present embodiment. The ultrasonic diagnostic apparatus 10 performs two-way simultaneous transmission, and each transmission waveform (transmission beam) is generated by TxDBF (transmission digital beam former) 12 and 14. The generated waveforms are the same waveform. That is, a waveform is generated in which both phase patterns match and the amplitudes match or are similar. As a result, the center frequencies of both transmission signals coincide with each other. The transmission waveform is generated by performing pulse expansion corresponding to pulse compression performed at the time of reception. The generated waveforms are added by an adder 16 and converted into an analog signal by a D / A (digital / analog converter) 18. Then, the signal is amplified to an appropriate size by the transmission amplifier 20 and then output to the piezoelectric element array 22. Generation of a transmission waveform and transmission of a corresponding ultrasonic wave are repeated at regular intervals.

  The piezoelectric element array 22 is an apparatus provided in an ultrasonic probe, in which a plurality of piezoelectric elements are linearly or convexly arranged in a one-dimensional or two-dimensional manner. Each piezoelectric element vibrates according to the input electric signal and generates an ultrasonic wave. And when it is vibrated by the ultrasonic wave reflected from the diagnostic object, an electrical signal corresponding to the vibration is output.

  The reception amplifier 24 inputs and amplifies the reception signal output from the piezoelectric element array 22, and the A / D (analog / digital converter) 26 converts the signal into digital. Received signals from the respective ultrasonic transducers converted into digital signals are input to RxDBF (received digital beam former) 28 and 42 and synthesized. The RxDBF 28 generates a reception signal (reception beam) corresponding to the transmission signal of the TxDBF 12, and the RxDBF 42 extracts a reception signal corresponding to the transmission signal of the TxDBF 14.

  The reception signal phased and added by the RxDBF 28 is subjected to pulse compression by a PC (pulse compression filter) 30 and output to the detector 32, and the detector 32 performs detection processing of the reception signal. The signal detected by the detector 32 is output to the black and white echo processing unit 34 and the color Doppler processing unit 36. The black and white echo processing unit 34 generates a black and white tomographic image (B mode image) for the scanning plane based on the received signals that are successively input. Further, the color Doppler processing unit 36 obtains a blood flow distribution in the direction based on the analysis of the phase change of a plurality of received signals in one direction, and further repeats the process for the scanning plane to thereby obtain a two-dimensional blood flow distribution. Generate an image. Similarly, the reception signal input to the RxDBF 42 is processed by the PC 44, the detector 46, the black and white echo processing unit 48, and the color Doppler processing unit 50. The PCs 30 and 44 can also be arranged in front of the RxDBFs 28 and 42, respectively.

  The image data generated by the monochrome echo processing units 34 and 48 and the color Doppler processing units 36 and 50 are input to a DSC (digital scan converter) 40. The DSC 40 performs data conversion in accordance with the display format of the display device 52 and outputs data to the display device 52. Thus, the display 52 displays a color Doppler image in which a color blood flow image is superimposed on a black and white tomographic image.

  The configuration of the ultrasonic diagnostic apparatus 10 illustrated in FIG. 1 can be variously modified. As an example, FIG. 2 shows an example in which received signal processing is realized by a single system configuration. 2, the same or corresponding components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  The ultrasonic diagnostic apparatus 60 shown in FIG. 2 is the same as the ultrasonic diagnostic apparatus 10 of FIG. 1 in that transmission signals that are simultaneously transmitted in different directions by the TxDBFs 12 and 14 are generated. However, the corresponding received signal is processed only by the RxDBF 62, the PC 64, the detector 66, the black and white echo processing unit 68, and the color Doppler processing unit 70, and is output to the DSC 40. This is because time-division processing is performed on received signals in two directions by increasing the processing capability of the RxDBF 62. That is, the A / D 26 output is subjected to reception signal processing corresponding to TxDBF12 and simultaneously stored in a separate memory, and when the signal processing is completed, the signal stored in the memory is input to correspond to TxDBF14. By performing the received signal processing, the received signals in two directions are processed by one system of receiving device. The memory can be installed immediately after the piezoelectric element array 22 or can be installed immediately after the reception amplifier 24. In addition, it is possible to further increase the number of received beams by applying conventional multi-directional simultaneous reception technology.

  FIG. 3 is a diagram illustrating a scanning example of a transmission beam performed by the ultrasonic diagnostic apparatus 10 illustrated in FIG. Here, the transmission of a series of a plurality of transmission beams (collectively referred to as a packet) performed simultaneously in two directions is repeated N times while changing the transmission direction so as to cover the fan-shaped scanning plane 80. Each of (a), (b), (c), (d), (e), and (f) shown in FIG. 3 shows the first, second, n, n + 1, n + 2, and N (where n = N / 2) packets. The transmission direction will be described. The fan shape of the scanning surface 80 has an opening angle 82 set to 90 degrees, and the first, second,. . . , N packets are scanned in the area to the left of the center line 84, and the (n + 1) th, n + 2,. . . , N packets are scanned on the right side of the center line 84.

  FIG. 3A illustrates transmission of the first packet. Here, the transmission beam 86 is transmitted to the left end side of the scanning plane 80, and the transmission beam 88 is transmitted in the direction in which the angle 85 formed by the transmission beam 86 is set to 22.5 degrees. Each transmission beam is repeatedly transmitted at a predetermined time interval, and the corresponding reception beam is received.

  In the subsequent transmission of the second packet in FIG. 3B, transmission beams 90 and 92 are transmitted. The transmission beams 90 and 92 are transmitted by changing the direction to the right side by about 22.5 / n degrees from the transmission beams 86 and 88 of the first packet, respectively. Similarly, in each packet, the transmission beam is transmitted a plurality of times by rotating to the right by about 22.5 / n degrees. In the n-th packet shown in FIG. 3C, the transmission beams 94 and 96 are transmitted in the direction rotated to the right by about 22.5 degrees from the transmission beams 86 and 88 of the first packet. Thereby, the scanning of the left half area of the scanning surface 80 is completed.

  In the (n + 1) th packet shown in FIG. 3D, the transmission beam 98 is transmitted along the center line 84 of the scanning plane 80, and the transmission beam 100 is transmitted in a direction rotated right by 22.5 degrees. ing. In the subsequent n + 2 packet, the transmission beams 102 and 104 are transmitted in a direction slightly rotated to the right as shown in FIG. In this way, the scanning of the right half area of the scanning surface 80 is repeated. In the last Nth packet, the transmission beams 106 and 108 are transmitted in the center direction and the right end direction in the right half region of the scanning plane 80.

  By this series of scanning, the transmission beam is struck over the entire scanning surface 80. In scanning, the transmission beams in the two directions are separated by 22.5 degrees because the interference between the two beams cannot be ignored if the two directions are too close. Also, the scanning of the left half area is completed first, and then the scanning of the right half area is completed. The transmission beam 94 in the nth packet in FIG. 3C and the first packet in FIG. This is because the difference in transmission time with the transmission beam 88 is shortened so that the connection between the two becomes smooth.

  Next, transmission energy in ultrasonic transmission will be described using the schematic diagram of FIG. FIG. 4A is a reference diagram for explaining the setting of transmission energy when transmission is performed only in one direction, and FIGS. 4B and 4C show the setting of transmission energy in two directions transmitted simultaneously. It is a figure explaining. The horizontal axis represents time, and the vertical axis represents the magnitude of the transmission voltage.

In FIG. 4A, the transmission beam is transmitted over time T at voltage V, and the transmission energy P is proportional to V ² T. On the other hand, in the two transmission beams shown in FIGS. 4B and 4C, transmission is performed over T ′ = 2 * T with a voltage of V ′ = V / 2. Each transmission energy is (V / 2) ² * 2 * T = P / 2, and a total of P energy is transmitted. In other words, the transmission energy is limited to the same level as in the conventional case by performing transmission with half the transmission energy in each direction. Thereby, it becomes possible to maintain the temperature rise of an ultrasonic probe to the same extent as before.

  FIG. 5 is a diagram for explaining a mode for increasing detection sensitivity by a pulse compression technique. As described with reference to FIG. 4, if ultrasonic transmission is performed simultaneously in a plurality of directions while maintaining the total energy, the detection sensitivity decreases in each direction by the amount of energy reduction. In order to compensate for this, here, a technique of pulse compression using a frequency-modulated wave is introduced.

  FIGS. 5A to 5D are graphs in which the horizontal axis represents time and the vertical axis represents frequency, and each shows an example of frequency modulation performed on a transmission signal. FIG. 5A shows an example of frequency modulation in which the frequency increases linearly from f1 to f2 as time progresses from t1 to t2. FIG. 5B shows an example of frequency modulation in which the frequency linearly decreases from f2 to f1 as time advances from t1 to t2. The frequency modulation may be performed nonlinearly with respect to time, and FIG. 5C illustrates an example in which the frequency increases nonlinearly from f1 to f2 as time progresses from t1 to t2. d) represents an example in which the frequency decreases nonlinearly from f2 to f1.

  When a reflected signal obtained by transmitting a frequency-modulated signal is received, correlation processing with a reference signal or matched filter processing is performed in the PCs 30 and 44 shown in FIG. Can be obtained. Thereby, it becomes possible to detect and compensate for the energy decrease. The frequency modulation can be different for each direction. Thereby, it becomes possible to suppress the influence of the interference of the transmission / reception signal between each direction.

  Subsequently, an advantage when the transmission waveforms in the respective directions are made equal will be described with reference to FIG. FIG. 6 is a graph in which the horizontal axis represents the depth direction (time direction) and the vertical axis represents the frequency, and shows two schematic Doppler shift frequency patterns 110 and 112 obtained by reception. The Doppler shift frequency pattern 110 is when the blood flow velocity is relatively slow. In this case, it can be detected by the frequency band −1/2 PRT to 1/2 PRT defined by the pulse transmission interval PRT of the transmission signal.

  On the other hand, the Doppler shift frequency pattern 112 shows a case where the blood flow velocity is relatively high. Here, the depth d1 to d2 exceeds 1/2 PRT, and the aliasing pattern 112a is generated on the −1/2 PRT side due to aliasing. In such a case, it is desirable to perform aliasing correction with the folded pattern 112a representing the original speed.

  The magnitude of the Doppler shift frequency generally depends on the center frequency of the transmission waveform. Therefore, in the waveforms having different center frequencies, the frequencies corresponding to the folding frequencies are different. For this reason, it becomes necessary to individually correct the value of the folding frequency in each direction, and the processing becomes complicated. Therefore, here, by transmitting ultrasonic beams having the same transmission waveform with the same center frequency, the Doppler shift characteristics are common, and the aliasing correction process can be simplified. Further, different frequency modulation processing may be performed for each direction. In this case, if the center frequency of the modulation frequency band (the center frequencies of f1 and f2 in FIGS. 5A to 5D) is made equal, the Doppler shift characteristics can be made common.

  Next, an aspect in which the focal lengths in the respective directions to be simultaneously transmitted are different from each other will be described with reference to FIGS. 7 and 8 are diagrams schematically showing focus setting of a transmission beam in one packet when two-way simultaneous transmission is performed. FIG. 7 shows an example in which the transmission focal point is 2, and FIG. 8 shows an example in which the transmission focal point is 3.

  FIG. 7A is a schematic diagram showing an example of focus setting when two-way simultaneous transmission is performed. Here, the transmission focus setting in each transmission is shown on the assumption that six transmissions from the first transmission to the sixth transmission are performed in one packet. The transmission focus is set for either the relatively shallow first transmission focus or the relatively deep second transmission focus.

  From the first transmission to the third transmission, that is, in the first half of all transmissions, one direction is fixed at the first transmission focus, and the other direction is fixed at the second transmission focus. Thereafter, the transmission focus is changed, and from the fourth transmission to the sixth transmission, that is, in the latter half of all transmissions, the one direction is fixed to the second transmission focus, and the other direction is changed. Is fixed at the first transmission focus. That is, the combinations of the transmission focal points of the two transmission beams are (1,2), (1,2), (1,2), (2,1), (2,1), (2,1). To be done.

  In addition to this, the focal length can be set in various ways. FIG. 7B is a schematic diagram illustrating another example of focus setting when two-way simultaneous transmission is performed. Here, the transmission focal points of the two transmission beams are sequentially replaced. That is, in six transmissions from the first transmission to the sixth transmission in one packet, the combinations of transmission focal points of two different directions of transmission beams transmitted simultaneously are (1, 2), (2, 1 ), (1,2), (2,1), (1,2), (2,1).

  In this way, by changing the focus setting in one packet, a combination of a plurality of received signals with a shallow portion detected with high accuracy and a plurality of received signals with a deep portion detected with high accuracy can be obtained. Processing for obtaining the velocity distribution, for example, autocorrelation processing, can be performed between received signals having the same focus setting. Further, it may be performed between received signals having different focus settings. In any case, by obtaining a velocity distribution based on a plurality of received signals having different focus settings, a color Doppler image with improved spatial resolution and detection sensitivity and improved spatial uniformity is obtained. Will be able to.

  Even if the number of transmission focal points is 3 or more, it can be implemented. FIG. 8A shows a case where the transmission focal point is set to one of a relatively shallow first transmission focal point, a medium second transmission focal point, and a relatively deep third transmission focal point to perform two-way simultaneous transmission. It is a figure explaining one aspect | mode. Here, in the six transmissions from the first transmission to the sixth transmission, the combinations of transmission focal points of two different transmission beams transmitted simultaneously are (1, 2), (1, 2), ( 2,3), (2,3), (3,1), (3,1). That is, each transmission focus is sequentially changed every two transmissions obtained by dividing the total number of transmissions of 6 by the transmission focus number of 3.

  FIG. 8B is a diagram for explaining another example when three transmission focal points are similarly set. Here, in six transmissions from the first transmission to the sixth transmission, the combinations of transmission focal points of two different transmission beams transmitted simultaneously are (1, 2), (2, 3), ( 3, 1), (1, 2), (2, 3), (3, 1). That is, each transmission focus is sequentially changed for each transmission. By increasing the number of transmission focal points in this manner, it is possible to further improve the spatial uniformity of the entire scanning region as compared with the two cases.

  FIG. 9 is a diagram for explaining the delay time setting of the ultrasonic transducer when the transmission focus is changed. The vertical axis in the figure is the depth direction, and the first transmission focal point 122 is set at a relatively shallow position below the probe surface 120 and the second transmission focal point 124 is set at a relatively deep position. A transmission waveform 126 in the ultrasonic transducer at the center of the probe is shown above the probe surface 120.

  When the focus is set to the first transmission focus 122, the transmission delay time of the ultrasonic waves from the respective ultrasonic transducers is set so that the arrival times at the first transmission focus are equal. Therefore, the equiphase surface 128 for the first transmission focal point is formed in an arc shape with the first transmission focal point 122 as the center. Similarly, the equiphase surface 130 for the second transmission focus is formed in an arc shape with the second transmission focus 124 as the center. Thereby, in each transmission focus, generation | occurrence | production of the phase error accompanying propagation time is suppressed, and a highly accurate detection is attained.

  Here, the setting of transmission energy when performing multi-directional simultaneous transmission will be described with reference to FIGS. FIG. 10 shows an example in which the transmission focus is set to the same depth in both directions when performing two-way simultaneous transmission, and FIG. 11 shows the transmission focus being set to different depths when performing two-way simultaneous transmission. This is an example.

  In FIG. 10, the transmission beams 142 and 144 are simultaneously transmitted from the probe 140 in different directions. The transmission focal point 146 of the transmission beam 142 and the transmission focal point 148 of the transmission beam 144 are set to the same depth. The transmission beams 142 and 144 are both transmitted with energy of E / 2. In other words, the total energy E input to the probe 140 is split in half and used to transmit the transmission beams 142 and 144. This is because the energy required for the transmission beam is generally larger as the transmission focal point is deeper. Therefore, the maximum energy E that can be input is equal to the transmission beams 142 and 144 having the same transmission focal point 146 and 148 depth. Because it is divided.

  On the other hand, in FIG. 11, the transmission beams 150 and 152 transmitted from the probe 140 in different directions have different transmission focal depths. That is, the transmission beam 150 is set to a relatively deep transmission focus 154 and the transmission beam 152 is set to a relatively shallow transmission focus 156. For this reason, out of the total energy E that can be input, for example, 3/5 is input to the transmission beam 150 and 2/5 is input to the transmission beam 152. As a result, a relatively large received signal can be obtained from the transmission beam 150, which is mainly used for detailed measurement at a deep position, despite the beam expansion and attenuation.

  In the example shown in FIGS. 7 and 8, the focal points of the two directions of transmission beams transmitted simultaneously are set to be different from each other. This is because, as shown in FIG. 11, relatively high energy can be input to a transmission beam having a deep transmission focal point.

  FIG. 12 is a diagram illustrating an energy input mode when transmission is performed according to the example illustrated in FIG. 11 under the transmission focus setting illustrated in FIG. 7B. The format of the figure is the same as that of FIG. 4, the horizontal axis represents time, and the vertical axis represents the magnitude of the transmission voltage. 4A shows a conventional general transmission mode, and FIGS. 4B and 4C show an example in which two-way simultaneous transmission is performed.

In FIG. 4A, ultrasonic transmission of energy P ₀ is performed at a voltage V ₀ for a short time T ₀ every pulse transmission time PRT. On the other hand, as shown in FIGS. 4B and 4C, in each direction in which two-way simultaneous transmission is performed, ultrasonic waves are applied at a voltage V ₁ (V ₁ <V ₂ ) for each pulse transmission time PRT. Transmission is performed. The transmission time is T ₁ when the transmission focus is shallow, and T ₂ (T ₁ <T ₂ ) when the transmission focus is deep. Then, the transmission times of T ₁ and T ₂ are also switched in response to the transmission focus being switched for each transmission within one packet. As a result, the magnitude of transmission energy repeats P ₁ and P ₂ (P ₁ <P ₂ ) alternately. When the magnitude of the total energy is P ₀ , the magnitudes of P ₁ and P ₂ may be determined under the condition of P ₁ + P ₂ = P ₀ .

  In the above description, the simultaneous transmission in a plurality of directions has been described by specifically taking the case of two directions as an example. However, as a matter of course, the present invention can also be applied to the case of three or more directions.

  In the color Doppler diagnosis, an ROI (region of interest) to be measured may be set in order to reduce the scanning region. In this case, the transmission focus may be set in conjunction with the ROI shape.

  Furthermore, the present technology can be widely extended not only to two-dimensional diagnosis but also to three-dimensional diagnosis. That is, a three-dimensional velocity distribution can be obtained by repeating a plurality of transmission / reception processes simultaneously performed in multiple directions so as to cover a predetermined three-dimensional scanning region. In the three-dimensional case, scanning generally requires time, but the use of this technique makes it possible to increase the frame rate.

It is a block diagram which shows the structural example of an ultrasonic diagnosing device. It is a block diagram which shows another structural example of an ultrasonic diagnosing device. It is a figure which shows the example of a scan by two-way simultaneous transmission. It is a schematic diagram explaining transmission energy. It is a figure which shows the modulation frequency characteristic of frequency modulation. It is a figure explaining an aliasing process. It is a figure which shows the example of an aspect which switches two transmission focus. It is a figure which shows the example of an aspect which switches three transmission focus. It is a figure which shows the relationship between a transmission focus and delay time. It is a figure which shows the example which makes the transmission focal distance of 2 directions equal. It is a figure which shows the example which varies the transmission focal distance of 2 directions. It is a figure explaining transmission energy switching corresponding to focus switching.

Explanation of symbols

  10 Ultrasonic Diagnostic Equipment, 12, 14 TxDBF, 16 Adder, 18 D / A, 20 Transmitting Amplifier, 22 Piezoelectric Array, 24 Receiving Amplifier, 26 A / D, 28, 42 RxDBF, 30, 44 PC, 32 Detection 34, 48 Monochrome echo processing unit, 36, 50 Color Doppler processing unit, 40 DSC, 52 display.

Claims (8)

An acquisition unit that transmits a pulse-type ultrasonic wave simultaneously to a plurality of directions and receives a reflected wave from a reflector a plurality of times, and obtains a reception signal for a plurality of times for each direction;
Calculation means for calculating a spatial distribution of the reflector velocity in each direction based on a phase analysis between the received signals;
With
An ultrasonic diagnostic apparatus characterized in that pulse-type ultrasonic waves transmitted simultaneously in a plurality of directions by an acquisition means have center frequencies set equal to each other. The ultrasonic diagnostic apparatus according to claim 1,
The acquisition means repeats the acquisition of the received signal while changing the transmission direction of the pulse-type ultrasound so as to scan the set scanning region,
The ultrasonic diagnostic apparatus characterized in that the calculation means obtains a spatial distribution of the reflector velocity in the scanning region. The ultrasonic diagnostic apparatus according to claim 1,
In the analysis of the phase relationship by the calculating means, an aliasing process is performed with the same aliasing frequency setting for each direction. The ultrasonic diagnostic apparatus according to claim 1,
An ultrasonic diagnostic apparatus characterized in that the ultrasonic transmission in the acquisition means is performed at different focal lengths in each direction. The ultrasonic diagnostic apparatus according to claim 4,
2. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic transmission in the acquisition unit is performed with different energy intensities corresponding to focal lengths in each direction. The ultrasonic diagnostic apparatus according to claim 4,
An ultrasonic diagnostic apparatus characterized in that the focal length is changed at least once in a plurality of ultrasonic transmissions in each direction in the acquisition means. The ultrasonic diagnostic apparatus according to claim 1,
An ultrasonic diagnostic apparatus characterized in that the ultrasonic transmission in the acquisition means is performed with the same transmission waveform in each direction. The ultrasonic diagnostic apparatus according to claim 1,
An ultrasonic diagnostic apparatus characterized in that a pulse compression technique is used for ultrasonic transmission / reception in the acquisition means.

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